Water quality in the Northern Colorado Plateau Network: Water years 2019?2022

Water quality monitoring in National Park Service units of the Northern Colorado Plateau Network (NCPN) is made possible through partnerships between the National Park Service Inventory & Monitoring Division, individual park units, the U.S. Geological Survey, and the Utah Department of Environmental Quality. This report evaluates water quality data from site visits at 42 different locations within and around eight park units in Utah and Colorado from October 1, 2018 through September 30, 2022. Data are compared to state water quality standards for the purpose of providing information to park managers about potential water quality problems. Parks included for evaluation are Arches National Park (NP), Bryce Canyon NP, Canyonlands NP, Capitol Reef NP, Dinosaur National Monument (NM), Hovenweep NM, Timpanogos Cave NM, and Zion NP. Evaluation of water quality parameters relative to state water quality standards indicated that 21,644 (96.8%) of the 22,356 total designated beneficial-use evaluations completed for the period covered in this report met state water quality standards. The most common parameters that did not meet a standard include fecal indicator bacteria (Escherichia coli), water temperature, and total dissolved solids (TDS). While TDS can be an indicator of pollution, in NCPN parks, it mostly occurs downstream of rock outcrops that naturally increase TDS in streams. Phosphorus concentrations were often greater than acceptable thresholds but were rarely associated with indicators of impairment such as algal blooms, fish kills, or low dissolved oxygen. Sites monitored in Arches NP, Bryce Canyon NP, Capitol Reef NP, Dinosaur NM, Hovenweep NM, and Zion NP all had occurrences when fecal indicator bacteria concentrations were greater than associated state standards. State-coordinated plans to reduce waste contamination are in place for the North Fork Virgin River (Zion NP) and the Fremont River (Capitol Reef NP). The plans have resulted in a decrease in the number of chronic and acute standard violations at Zion. Elevated water temperatures occurred at sites in Canyonlands NP, Capitol Reef NP, and Zion NP. Water temperature is strongly correlated with air temperature in surface waters across the Colorado Plateau. Additional issues of management concern include low dissolved oxygen in Salt Wash at Wolfe Ranch (Arches NP) and Square Tower Spring (Hovenweep NM), as well as selenium in the Colorado River (Arches NP and Canyonlands NP). State-coordinated plans to reduce selenium concentrations in the Upper Colorado River basin are in place.